Adding failing tests for end event firing multiple times when copying a file more than once.

Here is a failing test illustrating the issue in #302.

I think this is related to using the filename as part of the event name when [added to the conflicter](https://github.com/yeoman/generator/blob/c57e4e10ecc63535dc97fb40db0f51ac0f807b42/lib/actions/actions.js#L287-L294) and [resolving the conflict](https://github.com/yeoman/generator/blob/c57e4e10ecc63535dc97fb40db0f51ac0f807b42/lib/util/conflicter.js#L58-L61).